The objective of evolved high speed packet access (HSPA+) and long term evolution (LTE) of universal terrestrial radio access (UTRA) and universal terrestrial radio access network (UTRAN) is to develop a radio access network for high data rate, low latency, packet optimization, and improved system capacity and coverage. In order to achieve these goals, an evolution of a radio interface and radio network architecture are being considered. In HSPA+, the air interface technology will still be based on code division multiple access (CDMA) but with more efficient physical layer architecture which may include independent channelization codes, (distinguished with regard to channel quality), and multiple-input multiple-output (MIMO). In LTE, orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) are proposed as the air interface technologies to be used in the downlink and the uplink, respectively.
H-ARQ has been adopted by several wireless communication standards, including third generation partnership project (3GPP) and 3GPP2. Besides radio link control (RLC) layer automatic repeat request (ARQ) function, H-ARQ improves throughput, compensates for link adaptation errors and provides efficient transmission rates through the channel. The delay caused by H-ARQ feedback, (i.e., a positive acknowledgement (ACK) or a negative acknowledgement (NACK)), is significantly reduced by placing the H-ARQ functionality in a Node-B rather than in a radio network controller (RNC). A user equipment (UE) receiver may combine soft bits of the original transmission with soft bits of subsequent retransmissions to achieve higher block error rate (BLER) performance. Chase combining or incremental redundancy may be implemented.
Asynchronous H-ARQ is used in high speed downlink packet access (HSDPA) and synchronous H-ARQ is used in high speed uplink packet access (HSUPA). In both HSDPA and HSUPA, radio resources allocated for the transmission are the number of codes at a certain frequency band based on one channel quality indication (CQI) feedback. There is no differentiation among channelization codes. Therefore, one HSDPA medium access control (MAC-hs) flow or one HSUPA medium access control (MAC-e/es) flow multiplexed from multiple dedicated channel MAC (MAC-d) flows is assigned to one H-ARQ process and one cyclic redundancy check (CRC) is attached to one transport block.
A new physical layer attribute introduced in HSPA+ includes MIMO and different channelization codes. New physical layer attributes introduced in LTE include MIMO and different subcarriers, (localized or distributed). With introduction of these new physical layer attributes, the performance of conventional single H-ARQ scheme and transport format combination (TFC) selection procedure should be changed. In a conventional single H-ARQ scheme, only one H-ARQ process is active at a time and a TFC of only one transport data block needs to be determined in each TTI. The conventional TFC selection procedure does not have the ability to make TFC selection for more than one data block for multiple H-ARQ processes.